U.S. patent application number 09/862926 was filed with the patent office on 2002-01-10 for classification of the surface structure of heat exchanger tubes by means of doppler radar spectroscopy.
Invention is credited to Mueller, Gett, Mueller, Wolfgang, Riedle, Joachim.
Application Number | 20020003426 09/862926 |
Document ID | / |
Family ID | 7643297 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003426 |
Kind Code |
A1 |
Mueller, Gett ; et
al. |
January 10, 2002 |
Classification of the surface structure of heat exchanger tubes by
means of doppler radar spectroscopy
Abstract
A method for the quick classification of structured inner and/or
outer surfaces of heat exchanger tubes by means of Doppler radar
spectroscopy. The measured variables to be determined from the
frequency spectra: Surface integral A, average value m and variance
S (or standard deviation .sigma.={square root}{square root over
(S)}) correlate directly with the geometric parameters of the
structure morphology. They permit direct conclusions regarding the
heat transfer characteristics (evaporation/condensation
performance) of the respective structure, in particular no tube
samples ready for use are needed for the heat transfer
classification.
Inventors: |
Mueller, Gett; (Neu-Ulm,
DE) ; Riedle, Joachim; (Bad Wurzach, DE) ;
Mueller, Wolfgang; (Laupheim, DE) |
Correspondence
Address: |
David G. Boutell
Flynn, Thiel
Boutell & Tanis, P.C.
2026 Rambling Road
Kalamazoo
MI
49008-1699
US
|
Family ID: |
7643297 |
Appl. No.: |
09/862926 |
Filed: |
May 22, 2001 |
Current U.S.
Class: |
324/644 |
Current CPC
Class: |
G01B 15/08 20130101;
F28F 13/18 20130101 |
Class at
Publication: |
324/644 |
International
Class: |
G01R 027/04; G01R
027/32 |
Foreign Application Data
Date |
Code |
Application Number |
May 24, 2000 |
DE |
100 25 574.4 |
Claims
What is claimed is:
1. A method for classifying the structured inner and/or outer
surface of heat exchanger tubes with a longitudinal welded seam,
wherein in each case a defined sample of the structured band, which
is provided for the manufacture of the heat exchanger tube, is
moved and subjected to a Doppler radar spectroscopy measurement
using electromagnetic waves (microwaves) in the frequency range of
1 to 100 GHz, whereby the following magnitudes are determined from
the standardized Doppler radar spectrum (standardized to the plain
tube): Surface integral A, average value m and variance S (or
standard deviation .sigma.={square root}{square root over
(S)}).
2. The method for classifying the structured inner and/or outer
surface of seamless heat exchanger tubes, wherein in each case a
defined sample is moved from the surface of the heat exchanger
tube, which surface is unrolled in a plane, and is subjected to a
Doppler radar spectroscopy measurement using electromagnetic waves
(microwaves) in the frequency range of 1 to 100 GHz, whereby the
following magnitudes are determined from the standardized radar
Doppler spectrum (standardized to the plain tube): Surface integral
A, average value m and variance S (or standard deviation
.sigma.={square root}{square root over (S)}).
3. A heat exchanger tube with structured inner and/or outer
surface, comprising the magnitudes determined according to the
method according to claim 1 or 2: Surface integral A and variance S
(or standard deviation .sigma.), whereby
1.times.10.sup.0.ltoreq.A.ltoreq.2.times.10.sup.4 and
1.times.10.sup.2.ltoreq.S.ltoreq.5.times.10.sup.5 (or
1.times.10.sup.1.ltoreq..sigma..ltoreq.1.times.10.sup.3.
4. The heat exchanger tube according to claim 3, wherein
1.times.10.sup.1.ltoreq.A.ltoreq.5.times.10.sup.3 and
1.times.10.sup.3.ltoreq.S.ltoreq.1.times.10.sup.5 (or
3.times.10.sup.1.ltoreq..sigma..ltoreq.5.times.10.sup.2).
5. A method of employing the magnitudes surface integral A and
variance S (or standard deviation .sigma.), which magnitudes are
determined according to the method according to claim 1 or 2, for
the classification of the heat exchanger tubes through correlation
with the heat transfer characteristic according to the heat
transfer coefficient .alpha..
6. The method according to claim 5, wherein with surfaces on which
condensation takes place, .alpha..sub.cond correlates with A or S
in such a manner that an increase of A or a reduction of S
indicates the desired increase of .alpha..sub.cond, namely
.alpha..sub.cond.about.A or .alpha..sub.cond.about.S.sup.-1, and
wherein the spectrum average value m lies above the Doppler radar
base frequency f.sub.0.
7. The method according to claim 5, wherein with surfaces on which
evaporation takes place, .alpha..sub.evap correlates with A or S in
such a manner that an increase of A or a reduction of S indicates
the desired increase of .alpha..sub.evap; namely
.alpha..sub.evap.about.A or .alpha..sub.evap.about.S.sup.-1, and
wherein the spectrum average value m lies below the Doppler radar
base frequency f.sub.0.
Description
FIELD OF THE INVENTION
[0001] The subject matter of the invention relates to a method for
classifying the structured inner and/or outer surface of heat
exchanger tubes which are seamless or have a longitudinal welded
seam.
BACKGROUND OF THE INVENTION
[0002] According to the state of the art, surface-structured tubes
are preferably utilized for heat transfer processes. These tubes
are usually manufactured without a seam or are provided with a
longitudinal welded seam. As a rule the tubes are copper tubes.
[0003] Tubes with a structured surface have a larger surface area
than plain tubes. Tubes with a large surface area are preferably
utilized in heat exchanger systems. The goal is to achieve enhanced
performance densities for smaller sized products and lighter weight
construction. For this it is necessary to improve the performance
of the individual tubes.
[0004] The classification of structured tubes is accomplished
usually at a high expense and with much time through the
determination and analysis of the geometric magnitudes identifying
the structure, such as structure heights and element angles.
Examples of geometric structure magnitudes are, among others,
described in detail in the EP 0 148 609. Therefore, for the
classification of a geometric surface structure many individual
measurements are needed. Besides the considerable technical
measuring requirements, an accumulation of measurement errors may
still occur.
[0005] To determine the heat transfer characteristics of a heat
exchanger tube, it is necessary to carry out extensive measurements
on individual tubes or bundles of tubes on a special heat-transfer
test facility. Based on the background of the enormously large
multitude of geometrical structured elements there arises the
demand for a clear technically measured classification of the
structure finenesses and their heat performance characteristics
utilizing equipment clearly less complex compared with the state of
the art.
SUMMARY OF THE INVENTION
[0006] The basic purpose of the invention is therefore to provide
in place of the expensive, heat transfer measurement of individual
tubes a method for the quick, clear and reproducible classification
of structured surfaces. In particular a technical measurement
capability operating without contact has been discovered and with
which it is not necessary for a tube sample ready for use to be
present.
[0007] This has been accomplished by providing a method for
classifying the structured inner and/or outer surface of heat
exchanger tubes with a longitudinal welded seam, wherein in each
case a defined sample of the structured band, which is provided for
the manufacture of the heat exchanger tube, is moved and subjected
to a Doppler radar spectroscopy measurement using electromagnetic
waves (microwaves) in the frequency range of 1 to 100 GHz, whereby
the following magnitudes are determined from the standardized
Doppler radar spectrum (standardized to the plain tube):
[0008] Surface integral A, average value m and variance S (or
standard deviation .sigma.={square root}{square root over (S)}) as
well as a method for classifying the structured inner and/or outer
surface of seamless heat exchanger tubes, wherein in each case a
defined sample is moved from the surface of the heat exchanger
tube, which surface is unrolled in a plane, and is subjected to a
Doppler radar spectroscopy measurement using electromagnetic waves
(microwaves) in the frequency range of 1 to 100 GHz, whereby the
following magnitudes are determined from the standardized Doppler
radar spectrum (standardized to the plain tube):
[0009] Surface integral A, average value m and variance S (or
standard deviation .sigma.={square root}{square root over
(S)}).
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic illustration of a Doppler radar
spectroscopy method employed in this invention;
[0011] FIG. 2 is a graph of frequency spectra standardized to a
plain tube;
[0012] FIG. 3a is a schematic representation of the surface
integral A;
[0013] FIG. 3b is a schematic representation of the average value
m; and
[0014] FIG. 3c is a schematic representation of the standard
deviation .sigma..
DETAILED DESCRIPTION
[0015] The measuring method of the Doppler radar spectroscopy is
schematically illustrated in FIG. 1. The electromagnetic waves sent
at a specific angle from a microwave sender 1 in the frequency
range of 1 to 100 GHz are thereby reflected by a moving sample 2,
are registered by a receiver 3, and evaluated in a unit 4. The
arrow indicates the direction of movement of the sample. (Regarding
the basics of the radar measuring technique, reference is made, for
example, to the book of M. Skolnik "Introduction to Radar Systems",
McGraw-Hill (1980), in particular Page 68 and the following
pages).
[0016] The resulting frequency shift based on the Doppler effect is
measured. The structured surface of the moving band causes a
geometric frequency spectrum increase in the reflected portion of
the original monochromatically incident electromagnetic wave. This
frequency or line spectrum increase is characteristic for the
geometric structure of the surface and is noticeable after a
Fourier frequency analysis of the reflected signal as a frequency
spectrum in the range of the Doppler base frequency f.sub.0
determined by the test parameters (compare the frequency spectra
according to FIG. 2, which will be discussed later on, and which
show spectra each standardized to the plain tube as a function of
the Doppler shift (Hz)).
[0017] The following magnitudes are defined:
[0018] Surface integral A (compare schematic illustration in FIG.
3a),
[0019] average value m (compare FIG. 3b) and as measurement for the
width
[0020] variance S (compare FIG. 3c)
[0021] (or standard deviation .sigma.={square root}{square root
over (S)}).
[0022] These magnitudes can be illustrated mathematically in the
following manner:
[0023] If f(x) is the distribution function of the Doppler radar
frequencies x (standardized to a plain tube surface), that is, the
Doppler radar spectrum of a structure to be examined, then the
following applies: 1 Surface integral A - .infin. .infin. f ( x ) x
expected value or average value m - .infin. .infin. x f ( x ) x -
.infin. .infin. f ( x ) x variance S - .infin. .infin. ( x - m ) 2
f ( x ) x - .infin. .infin. f ( x ) x standard deviation S
[0024] (compare, for example, Bronstein/Semendjajew: "Taschenbuch
der Mathematik" (22.sup.nd Edition, 1985), Page 665 to 668).
[0025] The method of the Doppler radar spectroscopy has up to now,
for example, been utilized to examine the waviness of the surfaces
of oceans (compare, for example, D. R. Thomphson: "Probing the
Ocean Surface with Microwave Radar" in Johns Hopkins APL Technical
Digest, Volume 10, Number 4 (1989), Pages 332-338, or R. Romeiser:
"Doppler Spectra of the Radar Backscatter from the Sea Surface;
Obtained from a Three-Scale Composite Surface Model" in
International Geoscience and Remote Sensing Symposium (IGARSS) v 2,
1994, IEEEE, Piscataway, N.J., USA, 94CH3378-7, Page 729).
[0026] An application of the aforementioned subjects to the
examining of the structured surface of heat exchanger tubes is not
obvious for the man skilled in the art in particular due to varying
orders of magnitude and varying speeds of the test objects.
[0027] The surface of common heat exchanger tubes can be classified
according to the invention by the following areas:
[0028] 1.times.10.sup.0.ltoreq.A.ltoreq.2.times.10.sup.4, in
particular 1.times.10.sup.1.ltoreq.A.ltoreq.5.times.10.sup.3
[0029] 1.times.10.sup.2.ltoreq.S.ltoreq.5.times.10.sup.5, in
particular 1.times.10.sup.3.ltoreq.S.ltoreq.1.times.10.sup.5
[0030] (or 1.times.10.sup.1.ltoreq..sigma..ltoreq.1.times.10.sup.3,
in particular
3.times.10.sup.1.ltoreq..sigma..ltoreq.5.times.10.sup.2).
[0031] Within the scope of the invention it is found furthermore
advantageously that a clear and reproducible correlation exists
between the macroscopic surface topography, the specific parameter
heat transfer coefficient .alpha. and the objective, integral
characteristics of the Doppler radar spectra like surface integral
A, average value m, variance S and standard deviation .sigma.. Of
particular importance is that the parameters of the Doppler radar
spectra are suited for the heat transfer classification without
requiring a detailed knowledge of the geometric sizes of the
respective surface structures or tube samples ready for use.
[0032] The method of the Doppler radar spectroscopy is therefore
well suited to classify any desired surface structures which are
used, for example, to improve the specific thermal output of tubes
for the heat transfer, in view of the to be expected thermal output
of the tubes. The inventive relationship between the measured
variables obtained through Doppler radar spectroscopy and the
specific heat transfer performance of a tube sample ready for use
is distinguished by an excellent reproducing ability of the data.
The apparatus and time input is clearly lower compared with the
state of the art.
[0033] In the case of tubes with structures, which are preferably
utilized for use in liquifying processes, in particular in
structures with sharp, convex edges (compare DE 44 04 357 C1), it
has been shown that the Doppler spectrum average value m shifts to
frequencies above the Doppler base frequency f.sub.0, and that an
increase of the heat transfer coefficient .alpha..sub.cond equals
the increasing surface integral A of the Doppler radar spectrum.
The variance S and the standard deviation .sigma.decrease at the
same time.
[0034] In the case of tubes with structures, which are preferably
utilized in evaporation processes, in particular in undercut,
cavity-like structures, it has been shown that a Doppler spectrum
average value m shifts to frequencies below the Doppler base
frequency f.sub.0, and that an increase of the heat transfer
coefficient .alpha..sub.evap equals the increasing surface integral
A of the Doppler radar spectrum. The variance S and the standard
deviation .sigma. decrease at the same time.
[0035] The invention will be discussed in greater detail in
connection with the following exemplary embodiments:
[0036] 1. Heat exchanger tubes of copper with an outside diameter
of 9.52 mm. (3/8") and a core wall thickness of 0.30 mm, which heat
exchanger tubes are provided with a longitudinal welded seam, were
examined according to the following Table 1. For example, a plain
tube, a tube with a single inner fin structure and a tube with a
double inner fin structure are listed.
1 TABLE 1 TUBE WITH TUBE WITH PLAIN SINGLE INNER DOUBLE INNER TUBE
FIN STRUCTURE FIN STRUCTURE Tube 9.52 mm 9.52 mm 9.52 mm Dimension
(3/8") (3/8") (3/8") Fin Height -- 0.20 mm 0.20 mm Core Wall 0.30
mm 0.30 mm 0.30 mm Thickness 1. Finning No. of Fins -- 60 58 Angle
Helix -- .sup. 18.degree. .sup. 30.degree. 2. Finning No. of Fins
-- -- 80 Angle Helix -- -- -10.degree.
[0037] Copper alloys, aluminum, aluminum alloys and steel and
special steel continue to be preferred as materials for the
tubes.
[0038] Both the geometric sizes and also the thermal output were
determined in the single tube test facility. The heat transfer
measurements in the liquifying process resulted in the sequence
plain tube, tube with a single fin structure and tube with a double
fin structure in the performance relationships illustrated in Table
2a.
[0039] Parallel thereto, samples of bands used for the manufacture
of the tubes were each mounted to a moving sample carrier. The
plain surface or the inner structures were subsequently analyzed
with the help of the Doppler radar spectroscopy. The examination
was done with a 94 GHz radar module at a speed of the sample
carrier of 2 m/sec.
[0040] FIG. 2 shows the Doppler radar spectra obtained in the case
of the exemplarily listed tubes. The illustrated results are
standardized to the spectrum of the plain tube.
[0041] The spectrum (a) relates to the tube with a single fin
structure, the spectrum (b) to the tube with the double fin
structure.
[0042] For the parameters surface integral A, variance S and
standard deviation .sigma. result the following values according to
the Table 2b.
[0043] The good agreement of the ratio numbers regarding the
.alpha..sub.cond determined by heat transfer measurements and the
surface integrals A determined from Doppler radar spectra are
clearly noticeable.
[0044] The reciprocal numbers for S (or .sigma.) at the same time
correctly reproduce the relationship tendency in the performance
data.
[0045] Furthermore the determined Doppler spectrum average values m
lie above the Doppler base frequency f.sub.0 registered for the
plain tube, which is characteristic for condensation tubes.
[0046] 2. A plain tube, a tube with a single inner fin structure
and a tube with a double inner fin structure, as they are utilized
for evaporation processes, were examined in a second exemplary
embodiment (compare the following Table 3).
2 TABLE 3 TUBE WITH TUBE WITH PLAIN SINGLE INNER DOUBLE INNER TUBE
FIN STRUCTURE FIN STRUCTURE Tube 9.52 mm 9.52 mm 9.52 mm Dimension
(3/8") (3/8") (3/8") Fin Height -- 0.20 mm 0.20 mm Core Wall 0.30
mm 0.24 mm 0.22 mm Thickness 1. Finning No. of Fins -- 55 45 Angle
Helix -- .sup. 34.degree. .sup. 0.degree. 2. Finning No. of Fins --
-- 82 Angle Helix -- -- .sup. 42.degree.
[0047] The heat transfer measurements in the evaporation process in
the sequence plain tube, tube with single fin structure and tube
with double fin structure resulted in the performance relationships
illustrated in the Table 4a.
[0048] Samples of the bands used for the manufacture of the tubes
were parallel thereto analyzed with the help of the Doppler radar
spectroscopy. For the parameters surface integral A, variance S and
standard deviation .sigma.result the following values according to
Table 4b.
[0049] The ratio of surface integrals A, determined from the
Doppler radar spectra, just like the reciprocal values for S (or
.sigma.), correctly reproduce the tendency of the ratios of the
heat transfer coefficient .alpha..sub.evap. At the same time the
Doppler spectrum average values m lying below the Doppler base
frequency f.sub.0 indicate that we are dealing with structures
particularly suited for evaporation processes.
[0050] Thus the invention offers the possibility to draw from the
measured variables A, S (or .sigma.), m direct conclusions
regarding the evaporating and liquifying performance of the
respective surface structure.
3 TABLE 2a Plain Tube Measured Single Finned Tube Double Finned
Tube Value Measured Measured Heat Value Value Transfer Heat Heat
Coef- Transfer Transfer Mass ficient Ratio Coefficient Ratio
Coefficient Ratio Flow .alpha..sub.cond Ratio .alpha..sub.cond
Ratio .alpha..sub.cond Ratio 200 2400 1 3700 1.5 5200 2.2 300 3000
1 4400 1.5 6500 2.2 400 3500 1 5000 1.4 8000 2.3 500 4200 1 5800
1.4 9400 2.2 600 4900 1 6900 1.4 10900 2.2 700 5600 1 8000 1.4
12600 2.3 in kg/m.sup.2s in W/m.sup.2K in W/m.sup.2K in
W/m.sup.2K
[0051]
4 TABLE 2b Single Double Plain Tube Finned Tube Finned Tube
Measured Measured Measured Value Ratio Value Ratio Value Ratio
Surface 26 1 41 1.6 63 2.4 Integral A Variance 93025 1 50703 1.8
35601 2.6 S Std. 305 1 225 1.4 189 1.6 Deviation .sigma. Average
626 -- 643 -- 635 -- value m (f.sub.0)
[0052]
5 TABLE 4a Plain Tube Measured Double Finned Tube Value Single
Finned Tube Measured Heat Measured Value Transfer Value Heat Coef-
Heat Transfer Transfer Mass ficient Ratio Coefficient Ratio
Coefficient Ratio Flow .alpha..sub.evap Ratio .alpha..sub.evap
Ratio .alpha..sub.evap Ratio 140 2600 1 5800 2.2 6200 2.4 160 2700
1 5600 2.1 6800 2.5 180 2900 1 5400 1.9 7250 2.5 200 3000 1 5200
1.7 7700 2.6 220 3000 1 5100 1.7 8000 2.7 in in W/m.sup.2K in
W/m.sup.2K in W/m.sup.2K kg/m.sup.2s
[0053]
6 TABLE 4b Single Double Plain Tube Finned Tube Finned Tube
Measured Measured Measured Value Ratio Value Ratio Value Ratio
Surface 26 1 65 2.5 97 3.7 Integral A Variance 93025 1 38097 2.4
32469 2.9 S Std. 305 1 198 1.5 180 1.7 Deviation .sigma. Average
626 -- 614 -- 618 -- value m (f.sub.0)
* * * * *